Ejemplo n.º 1
0
  def test_validation(self):
    """Test that get_merge_timeout rejects invalid values of
    MERGE_TIMEOUT_OVERRIDE."""
    self._set_environment_values({
        'HARD_TIMEOUT_OVERRIDE': self.valid_hard_timeout,
        'MERGE_TIMEOUT_OVERRIDE': -1
    })

    with self.assertRaises(AssertionError):
      engine_common.get_merge_timeout(self.valid_merge_timeout)
Ejemplo n.º 2
0
  def test_correctness(self):
    """Test that get_merge_timeout returns what we expect."""
    # Basic sanity test.
    self.assertEqual(self.valid_merge_timeout,
                     engine_common.get_merge_timeout(self.valid_merge_timeout))

    # Test override works.
    override = 10
    self._set_environment_values({'MERGE_TIMEOUT_OVERRIDE': override})
    self.assertEqual(override,
                     engine_common.get_merge_timeout(self.valid_merge_timeout))
Ejemplo n.º 3
0
    def _merge_new_units(self, target_path, corpus_dir, new_corpus_dir,
                         fuzz_corpus_dirs, arguments, stat_overrides):
        """Merge new units."""
        # Make a decision on whether merge step is needed at all. If there are no
        # new units added by libFuzzer run, then no need to do merge at all.
        new_units_added = shell.get_directory_file_count(new_corpus_dir)
        if not new_units_added:
            stat_overrides['new_units_added'] = 0
            logs.log(
                'Skipped corpus merge since no new units added by fuzzing.')
            return

        # If this times out, it's possible that we will miss some units. However, if
        # we're taking >10 minutes to load/merge the corpus something is going very
        # wrong and we probably don't want to make things worse by adding units
        # anyway.
        merge_corpus = self._create_temp_corpus_dir('merge-corpus')

        merge_dirs = [new_corpus_dir]
        merge_dirs.extend(fuzz_corpus_dirs)

        # Merge the new units with the initial corpus.
        if corpus_dir not in merge_dirs:
            merge_dirs.append(corpus_dir)

        old_corpus_len = shell.get_directory_file_count(corpus_dir)

        new_units_added = 0
        try:
            result = self.minimize_corpus(
                target_path=target_path,
                arguments=arguments,
                input_dirs=merge_dirs,
                output_dir=merge_corpus,
                reproducers_dir=None,
                max_time=engine_common.get_merge_timeout(
                    launcher.DEFAULT_MERGE_TIMEOUT))

            launcher.move_mergeable_units(merge_corpus, corpus_dir)
            new_corpus_len = shell.get_directory_file_count(corpus_dir)
            new_units_added = new_corpus_len - old_corpus_len

            if result.logs:
                stat_overrides.update(
                    stats.parse_stats_from_merge_log(result.logs.splitlines()))
        except MergeError:
            logs.log_error('Merge failed.')

        stat_overrides['new_units_added'] = new_units_added

        logs.log('Stats calculated', stats=stat_overrides)

        # Record the stats to make them easily searchable in stackdriver.
        if new_units_added:
            logs.log('New units added to corpus: %d.' % new_units_added)
        else:
            logs.log('No new units found.')
Ejemplo n.º 4
0
def get_fuzz_timeout():
    """Get the maximum amount of time that should be spent fuzzing."""
    hard_timeout = engine_common.get_hard_timeout()
    merge_timeout = engine_common.get_merge_timeout(DEFAULT_MERGE_TIMEOUT)
    fuzz_timeout = hard_timeout - merge_timeout
    assert fuzz_timeout > 0, 'hard_timeout: %d merge_timeout: %d' % (
        hard_timeout, merge_timeout)

    return fuzz_timeout
Ejemplo n.º 5
0
def get_fuzz_timeout(is_mutations_run):
    """Get the fuzz timeout."""
    fuzz_timeout = (engine_common.get_hard_timeout() -
                    engine_common.get_merge_timeout(DEFAULT_MERGE_TIMEOUT) -
                    get_dictionary_analysis_timeout())

    if is_mutations_run:
        fuzz_timeout -= get_new_testcase_mutations_timeout()

    return fuzz_timeout
Ejemplo n.º 6
0
    def _merge_new_units(self, target_path, corpus_dir, new_corpus_dir,
                         fuzz_corpus_dirs, merge_corpus_dir, reproducers_dir,
                         arguments, stat_overrides):
        """Merge new units."""
        # Make a decision on whether merge step is needed at all. If there are no
        # new units added by libFuzzer run, then no need to do merge at all.
        new_units_added = shell.get_directory_file_count(new_corpus_dir)
        if not new_units_added:
            stat_overrides['new_units_added'] = 0
            logs.log(
                'Skipped corpus merge since no new units added by fuzzing.')
            return

        # If this times out, it's possible that we will miss some units. However, if
        # we're taking >10 minutes to load/merge the corpus something is going very
        # wrong and we probably don't want to make things worse by adding units
        # anyway.
        merge_dirs = fuzz_corpus_dirs[:]

        # Merge the new units with the initial corpus.
        if corpus_dir not in merge_dirs:
            merge_dirs.append(corpus_dir)

        old_corpus_len = shell.get_directory_file_count(corpus_dir)

        new_units_added = 0
        try:
            result = self._minimize_corpus_two_step(
                target_path=target_path,
                arguments=arguments,
                existing_corpus_dirs=merge_dirs,
                new_corpus_dir=new_corpus_dir,
                output_corpus_dir=merge_corpus_dir,
                reproducers_dir=reproducers_dir,
                max_time=engine_common.get_merge_timeout(
                    libfuzzer.DEFAULT_MERGE_TIMEOUT))

            libfuzzer.move_mergeable_units(merge_corpus_dir, corpus_dir)
            new_corpus_len = shell.get_directory_file_count(corpus_dir)
            new_units_added = new_corpus_len - old_corpus_len

            stat_overrides.update(result.stats)
        except (MergeError, engine.TimeoutError) as e:
            logs.log_warn('Merge failed.', error=repr(e))

        stat_overrides['new_units_added'] = new_units_added

        # Record the stats to make them easily searchable in stackdriver.
        logs.log('Stats calculated.', stats=stat_overrides)
        if new_units_added:
            logs.log('New units added to corpus: %d.' % new_units_added)
        else:
            logs.log('No new units found.')
Ejemplo n.º 7
0
    def __init__(self,
                 target_path,
                 config,
                 testcase_file_path,
                 input_directory,
                 afl_tools_path=None):
        """Inits the AflRunner.

    Args:
      target_path: Path to the fuzz target.
      config: AflConfig object.
      testcase_file_path: File to write crashes to.
      input_directory: Corpus directory passed to afl-fuzz.
      afl_tools_path: Path that is used to locate afl-* tools.
    """

        self.target_path = target_path
        self.config = config
        self.testcase_file_path = testcase_file_path
        self._input_directory = input_directory

        if afl_tools_path is None:
            afl_tools_path = os.path.dirname(target_path)

        # Set paths to afl tools.
        self.afl_fuzz_path = os.path.join(afl_tools_path, 'afl-fuzz')
        self.afl_showmap_path = os.path.join(afl_tools_path, 'afl-showmap')

        self._afl_input = None
        self._afl_output = None

        self.strategies = FuzzingStrategies()

        # Set this to None so we can tell if it has never been set or if it's just
        # empty.
        self._fuzzer_stderr = None

        self.initial_max_total_time = 0

        for env_var, value in config.additional_env_vars.iteritems():
            environment.set_value(env_var, value)

        self.showmap_output_path = os.path.join(fuzzer_utils.get_temp_dir(),
                                                self.SHOWMAP_FILENAME)
        self.merge_timeout = engine_common.get_merge_timeout(
            DEFAULT_MERGE_TIMEOUT)
        self.showmap_no_output_logged = False
Ejemplo n.º 8
0
def main(argv):
    """Run libFuzzer as specified by argv."""
    atexit.register(fuzzer_utils.cleanup)

    # Initialize variables.
    arguments = argv[1:]
    testcase_file_path = arguments.pop(0)
    target_name = arguments.pop(0)
    fuzzer_name = data_types.fuzz_target_project_qualified_name(
        utils.current_project(), target_name)

    # Initialize log handler.
    logs.configure(
        'run_fuzzer', {
            'fuzzer': fuzzer_name,
            'engine': 'libFuzzer',
            'job_name': environment.get_value('JOB_NAME')
        })

    profiler.start_if_needed('libfuzzer_launcher')

    # Make sure that the fuzzer binary exists.
    build_directory = environment.get_value('BUILD_DIR')
    fuzzer_path = engine_common.find_fuzzer_path(build_directory, target_name)
    if not fuzzer_path:
        # This is an expected case when doing regression testing with old builds
        # that do not have that fuzz target. It can also happen when a host sends a
        # message to an untrusted worker that just restarted and lost information on
        # build directory.
        logs.log_warn('Could not find fuzz target %s.' % target_name)
        return

    # Install signal handler.
    signal.signal(signal.SIGTERM, engine_common.signal_term_handler)

    # Set up temp dir.
    engine_common.recreate_directory(fuzzer_utils.get_temp_dir())

    # Setup minijail if needed.
    use_minijail = environment.get_value('USE_MINIJAIL')
    runner = libfuzzer.get_runner(fuzzer_path,
                                  temp_dir=fuzzer_utils.get_temp_dir())

    if use_minijail:
        minijail_chroot = runner.chroot
    else:
        minijail_chroot = None

    # Get corpus directory.
    corpus_directory = environment.get_value('FUZZ_CORPUS_DIR')

    # Add common arguments which are necessary to be used for every run.
    arguments = expand_with_common_arguments(arguments)

    # Add sanitizer options to environment that were specified in the .options
    # file and options that this script requires.
    set_sanitizer_options(fuzzer_path)

    # Minimize test argument.
    minimize_to = fuzzer_utils.extract_argument(arguments,
                                                MINIMIZE_TO_ARGUMENT)
    minimize_timeout = fuzzer_utils.extract_argument(
        arguments, MINIMIZE_TIMEOUT_ARGUMENT)

    if minimize_to and minimize_timeout:
        minimize_testcase(runner, testcase_file_path, minimize_to,
                          int(minimize_timeout), arguments, use_minijail)
        return

    # Cleanse argument.
    cleanse_to = fuzzer_utils.extract_argument(arguments, CLEANSE_TO_ARGUMENT)
    cleanse_timeout = fuzzer_utils.extract_argument(arguments,
                                                    CLEANSE_TIMEOUT_ARGUMENT)

    if cleanse_to and cleanse_timeout:
        cleanse_testcase(runner, testcase_file_path, cleanse_to,
                         int(cleanse_timeout), arguments, use_minijail)
        return

    # If we don't have a corpus, then that means this is not a fuzzing run.
    if not corpus_directory:
        load_testcase_if_exists(runner, testcase_file_path, fuzzer_name,
                                use_minijail, arguments)
        return

    # We don't have a crash testcase, fuzz.

    # Check dict argument to make sure that it's valid.
    dict_argument = fuzzer_utils.extract_argument(arguments,
                                                  constants.DICT_FLAG,
                                                  remove=False)
    if dict_argument and not os.path.exists(dict_argument):
        logs.log_error('Invalid dict %s for %s.' %
                       (dict_argument, fuzzer_name))
        fuzzer_utils.extract_argument(arguments, constants.DICT_FLAG)

    # If there's no dict argument, check for %target_binary_name%.dict file.
    if (not fuzzer_utils.extract_argument(
            arguments, constants.DICT_FLAG, remove=False)):
        default_dict_path = dictionary_manager.get_default_dictionary_path(
            fuzzer_path)
        if os.path.exists(default_dict_path):
            arguments.append(constants.DICT_FLAG + default_dict_path)

    fuzzing_strategies = []

    # Select a generator to use for existing testcase mutations.
    generator = _select_generator()
    is_mutations_run = generator != Generator.NONE

    # Timeout for fuzzer run.
    fuzz_timeout = get_fuzz_timeout(is_mutations_run)

    # Set up scratch directory for writing new units.
    new_testcases_directory = create_corpus_directory('new')

    # Get list of corpus directories.
    corpus_directories = get_corpus_directories(corpus_directory,
                                                new_testcases_directory,
                                                fuzzer_path,
                                                fuzzing_strategies,
                                                minijail_chroot)

    # Bind corpus directories in minijail.
    if use_minijail:
        artifact_prefix = constants.ARTIFACT_PREFIX_FLAG + '/'
    else:
        artifact_prefix = '%s%s/' % (constants.ARTIFACT_PREFIX_FLAG,
                                     os.path.abspath(
                                         os.path.dirname(testcase_file_path)))

    # Generate new testcase mutations using radamsa, etc.
    if is_mutations_run:
        new_testcase_mutations_directory = generate_new_testcase_mutations(
            corpus_directory, fuzzer_name, generator, fuzzing_strategies)
        corpus_directories.append(new_testcase_mutations_directory)
        if use_minijail:
            bind_corpus_dirs(minijail_chroot,
                             [new_testcase_mutations_directory])

    max_len_argument = fuzzer_utils.extract_argument(arguments,
                                                     constants.MAX_LEN_FLAG,
                                                     remove=False)
    if not max_len_argument and do_random_max_length():
        max_length = random.SystemRandom().randint(1, MAX_VALUE_FOR_MAX_LENGTH)
        arguments.append('%s%d' % (constants.MAX_LEN_FLAG, max_length))
        fuzzing_strategies.append(strategy.RANDOM_MAX_LENGTH_STRATEGY)

    if do_recommended_dictionary():
        if add_recommended_dictionary(arguments, fuzzer_name, fuzzer_path):
            fuzzing_strategies.append(strategy.RECOMMENDED_DICTIONARY_STRATEGY)

    if do_value_profile():
        arguments.append(constants.VALUE_PROFILE_ARGUMENT)
        fuzzing_strategies.append(strategy.VALUE_PROFILE_STRATEGY)

    if do_fork():
        max_fuzz_threads = environment.get_value('MAX_FUZZ_THREADS', 1)
        num_fuzz_processes = max(
            1,
            multiprocessing.cpu_count() // max_fuzz_threads)
        arguments.append('%s%d' % (constants.FORK_FLAG, num_fuzz_processes))
        fuzzing_strategies.append('%s_%d' %
                                  (strategy.FORK_STRATEGY, num_fuzz_processes))

    extra_env = {}
    if do_mutator_plugin():
        if use_mutator_plugin(target_name, extra_env, minijail_chroot):
            fuzzing_strategies.append(strategy.MUTATOR_PLUGIN_STRATEGY)

    # Execute the fuzzer binary with original arguments.
    fuzz_result = runner.fuzz(corpus_directories,
                              fuzz_timeout=fuzz_timeout,
                              additional_args=arguments + [artifact_prefix],
                              extra_env=extra_env)

    if (not use_minijail
            and fuzz_result.return_code == constants.LIBFUZZER_ERROR_EXITCODE):
        # Minijail returns 1 if the exit code is nonzero.
        # Otherwise: we can assume that a return code of 1 means that libFuzzer
        # itself ran into an error.
        logs.log_error(ENGINE_ERROR_MESSAGE, engine_output=fuzz_result.output)

    log_lines = fuzz_result.output.splitlines()
    # Output can be large, so save some memory by removing reference to the
    # original output which is no longer needed.
    fuzz_result.output = None

    # Check if we crashed, and get the crash testcase path.
    crash_testcase_file_path = None
    for line in log_lines:
        match = re.match(CRASH_TESTCASE_REGEX, line)
        if match:
            crash_testcase_file_path = match.group(1)
            break

    if crash_testcase_file_path:
        # Write the new testcase.
        if use_minijail:
            # Convert chroot relative path to host path. Remove the leading '/' before
            # joining.
            crash_testcase_file_path = os.path.join(
                minijail_chroot.directory, crash_testcase_file_path[1:])

        # Copy crash testcase contents into the main testcase path.
        shutil.move(crash_testcase_file_path, testcase_file_path)

    # Print the command output.
    log_header_format = ('Command: %s\n' 'Bot: %s\n' 'Time ran: %f\n')
    bot_name = environment.get_value('BOT_NAME', '')
    command = fuzz_result.command
    if use_minijail:
        # Remove minijail prefix.
        command = engine_common.strip_minijail_command(command, fuzzer_path)
    print(log_header_format % (engine_common.get_command_quoted(command),
                               bot_name, fuzz_result.time_executed))

    # Parse stats information based on libFuzzer output.
    parsed_stats = parse_log_stats(log_lines)

    # Extend parsed stats by additional performance features.
    parsed_stats.update(
        stats.parse_performance_features(log_lines, fuzzing_strategies,
                                         arguments))

    # Set some initial stat overrides.
    timeout_limit = fuzzer_utils.extract_argument(arguments,
                                                  constants.TIMEOUT_FLAG,
                                                  remove=False)

    expected_duration = runner.get_max_total_time(fuzz_timeout)
    actual_duration = int(fuzz_result.time_executed)
    fuzzing_time_percent = 100 * actual_duration / float(expected_duration)
    stat_overrides = {
        'timeout_limit': int(timeout_limit),
        'expected_duration': expected_duration,
        'actual_duration': actual_duration,
        'fuzzing_time_percent': fuzzing_time_percent,
    }

    # Remove fuzzing arguments before merge and dictionary analysis step.
    remove_fuzzing_arguments(arguments)

    # Make a decision on whether merge step is needed at all. If there are no
    # new units added by libFuzzer run, then no need to do merge at all.
    new_units_added = shell.get_directory_file_count(new_testcases_directory)
    merge_error = None
    if new_units_added:
        # Merge the new units with the initial corpus.
        if corpus_directory not in corpus_directories:
            corpus_directories.append(corpus_directory)

        # If this times out, it's possible that we will miss some units. However, if
        # we're taking >10 minutes to load/merge the corpus something is going very
        # wrong and we probably don't want to make things worse by adding units
        # anyway.

        merge_tmp_dir = None
        if not use_minijail:
            merge_tmp_dir = os.path.join(fuzzer_utils.get_temp_dir(),
                                         'merge_workdir')
            engine_common.recreate_directory(merge_tmp_dir)

        old_corpus_len = shell.get_directory_file_count(corpus_directory)
        merge_directory = create_merge_directory()
        corpus_directories.insert(0, merge_directory)

        if use_minijail:
            bind_corpus_dirs(minijail_chroot, [merge_directory])

        merge_result = runner.merge(
            corpus_directories,
            merge_timeout=engine_common.get_merge_timeout(
                DEFAULT_MERGE_TIMEOUT),
            tmp_dir=merge_tmp_dir,
            additional_args=arguments)

        move_mergeable_units(merge_directory, corpus_directory)
        new_corpus_len = shell.get_directory_file_count(corpus_directory)
        new_units_added = 0

        merge_error = None
        if merge_result.timed_out:
            merge_error = 'Merging new testcases timed out:'
        elif merge_result.return_code != 0:
            merge_error = 'Merging new testcases failed:'
        else:
            new_units_added = new_corpus_len - old_corpus_len

        stat_overrides['new_units_added'] = new_units_added

        if merge_result.output:
            stat_overrides.update(
                stats.parse_stats_from_merge_log(
                    merge_result.output.splitlines()))
    else:
        stat_overrides['new_units_added'] = 0
        logs.log('Skipped corpus merge since no new units added by fuzzing.')

    # Get corpus size after merge. This removes the duplicate units that were
    # created during this fuzzing session.
    stat_overrides['corpus_size'] = shell.get_directory_file_count(
        corpus_directory)

    # Delete all corpus directories except for the main one. These were temporary
    # directories to store new testcase mutations and have already been merged to
    # main corpus directory.
    if corpus_directory in corpus_directories:
        corpus_directories.remove(corpus_directory)
    for directory in corpus_directories:
        shutil.rmtree(directory, ignore_errors=True)

    if use_minijail:
        unbind_corpus_dirs(minijail_chroot, corpus_directories)

    # Apply overridden stats to the parsed stats prior to dumping.
    parsed_stats.update(stat_overrides)

    # Dump stats data for further uploading to BigQuery.
    engine_common.dump_big_query_data(parsed_stats, testcase_file_path,
                                      LIBFUZZER_PREFIX, fuzzer_name, command)

    # Add custom crash state based on fuzzer name (if needed).
    add_custom_crash_state_if_needed(fuzzer_name, log_lines, parsed_stats)
    for line in log_lines:
        print(line)

    # Add fuzzing strategies used.
    engine_common.print_fuzzing_strategies(fuzzing_strategies)

    # Add merge error (if any).
    if merge_error:
        print(data_types.CRASH_STACKTRACE_END_MARKER)
        print(merge_error)
        print(
            'Command:',
            get_printable_command(merge_result.command, fuzzer_path,
                                  use_minijail))
        print(merge_result.output)

    analyze_and_update_recommended_dictionary(runner, fuzzer_name, log_lines,
                                              corpus_directory, arguments)

    # Close minijail chroot.
    if use_minijail:
        minijail_chroot.close()

    # Record the stats to make them easily searchable in stackdriver.
    if new_units_added:
        logs.log('New units added to corpus: %d.' % new_units_added,
                 stats=parsed_stats)
    else:
        logs.log('No new units found.', stats=parsed_stats)
Ejemplo n.º 9
0
def main(argv):
  """Run libFuzzer as specified by argv."""
  atexit.register(fuzzer_utils.cleanup)

  # Initialize variables.
  arguments = argv[1:]
  testcase_file_path = arguments.pop(0)

  target_name = environment.get_value('FUZZ_TARGET')
  if arguments and arguments[0] == target_name:
    # Pop legacy fuzz target argument.
    arguments.pop(0)

  fuzzer_name = data_types.fuzz_target_project_qualified_name(
      utils.current_project(), target_name)

  # Initialize log handler.
  logs.configure(
      'run_fuzzer', {
          'fuzzer': fuzzer_name,
          'engine': 'libFuzzer',
          'job_name': environment.get_value('JOB_NAME')
      })

  profiler.start_if_needed('libfuzzer_launcher')

  # Make sure that the fuzzer binary exists.
  build_directory = environment.get_value('BUILD_DIR')
  fuzzer_path = engine_common.find_fuzzer_path(build_directory, target_name)
  if not fuzzer_path:
    return

  # Install signal handler.
  signal.signal(signal.SIGTERM, engine_common.signal_term_handler)

  # Set up temp dir.
  engine_common.recreate_directory(fuzzer_utils.get_temp_dir())

  # Setup minijail if needed.
  use_minijail = environment.get_value('USE_MINIJAIL')
  runner = libfuzzer.get_runner(
      fuzzer_path, temp_dir=fuzzer_utils.get_temp_dir())

  if use_minijail:
    minijail_chroot = runner.chroot
  else:
    minijail_chroot = None

  # Get corpus directory.
  corpus_directory = environment.get_value('FUZZ_CORPUS_DIR')

  # Add common arguments which are necessary to be used for every run.
  arguments = expand_with_common_arguments(arguments)

  # Add sanitizer options to environment that were specified in the .options
  # file and options that this script requires.
  set_sanitizer_options(fuzzer_path)

  # If we don't have a corpus, then that means this is not a fuzzing run.
  if not corpus_directory:
    load_testcase_if_exists(runner, testcase_file_path, fuzzer_name,
                            use_minijail, arguments)
    return

  # We don't have a crash testcase, fuzz.

  # Check dict argument to make sure that it's valid.
  dict_argument = fuzzer_utils.extract_argument(
      arguments, constants.DICT_FLAG, remove=False)
  if dict_argument and not os.path.exists(dict_argument):
    logs.log_error('Invalid dict %s for %s.' % (dict_argument, fuzzer_name))
    fuzzer_utils.extract_argument(arguments, constants.DICT_FLAG)

  # If there's no dict argument, check for %target_binary_name%.dict file.
  if (not fuzzer_utils.extract_argument(
      arguments, constants.DICT_FLAG, remove=False)):
    default_dict_path = dictionary_manager.get_default_dictionary_path(
        fuzzer_path)
    if os.path.exists(default_dict_path):
      arguments.append(constants.DICT_FLAG + default_dict_path)

  # Set up scratch directory for writing new units.
  new_testcases_directory = create_corpus_directory('new')

  # Strategy pool is the list of strategies that we attempt to enable, whereas
  # fuzzing strategies is the list of strategies that are enabled. (e.g. if
  # mutator is selected in the pool, but not available for a given target, it
  # would not be added to fuzzing strategies.)
  strategy_pool = strategy_selection.generate_weighted_strategy_pool(
      strategy_list=strategy.LIBFUZZER_STRATEGY_LIST,
      use_generator=True,
      engine_name='libFuzzer')
  strategy_info = pick_strategies(
      strategy_pool,
      fuzzer_path,
      corpus_directory,
      arguments,
      minijail_chroot=minijail_chroot)
  arguments.extend(strategy_info.arguments)

  # Timeout for fuzzer run.
  fuzz_timeout = get_fuzz_timeout(strategy_info.is_mutations_run)

  # Get list of corpus directories.
  # TODO(flowerhack): Implement this to handle corpus sync'ing.
  if environment.platform() == 'FUCHSIA':
    corpus_directories = []
  else:
    corpus_directories = get_corpus_directories(
        corpus_directory,
        new_testcases_directory,
        fuzzer_path,
        strategy_info.fuzzing_strategies,
        strategy_pool,
        minijail_chroot=minijail_chroot,
        allow_corpus_subset=not strategy_info.use_dataflow_tracing)

  corpus_directories.extend(strategy_info.additional_corpus_dirs)

  artifact_prefix = os.path.abspath(os.path.dirname(testcase_file_path))
  # Execute the fuzzer binary with original arguments.
  fuzz_result = runner.fuzz(
      corpus_directories,
      fuzz_timeout=fuzz_timeout,
      artifact_prefix=artifact_prefix,
      additional_args=arguments,
      extra_env=strategy_info.extra_env)

  if (not use_minijail and
      fuzz_result.return_code == constants.LIBFUZZER_ERROR_EXITCODE):
    # Minijail returns 1 if the exit code is nonzero.
    # Otherwise: we can assume that a return code of 1 means that libFuzzer
    # itself ran into an error.
    logs.log_error(ENGINE_ERROR_MESSAGE, engine_output=fuzz_result.output)

  log_lines = fuzz_result.output.splitlines()
  # Output can be large, so save some memory by removing reference to the
  # original output which is no longer needed.
  fuzz_result.output = None

  # Check if we crashed, and get the crash testcase path.
  crash_testcase_file_path = runner.get_testcase_path(log_lines)
  if crash_testcase_file_path:
    # Copy crash testcase contents into the main testcase path.
    shutil.move(crash_testcase_file_path, testcase_file_path)

  # Print the command output.
  bot_name = environment.get_value('BOT_NAME', '')
  command = fuzz_result.command
  if use_minijail:
    # Remove minijail prefix.
    command = engine_common.strip_minijail_command(command, fuzzer_path)
  print(engine_common.get_log_header(command, bot_name,
                                     fuzz_result.time_executed))

  # Parse stats information based on libFuzzer output.
  parsed_stats = parse_log_stats(log_lines)

  # Extend parsed stats by additional performance features.
  parsed_stats.update(
      stats.parse_performance_features(
          log_lines, strategy_info.fuzzing_strategies, arguments))

  # Set some initial stat overrides.
  timeout_limit = fuzzer_utils.extract_argument(
      arguments, constants.TIMEOUT_FLAG, remove=False)

  expected_duration = runner.get_max_total_time(fuzz_timeout)
  actual_duration = int(fuzz_result.time_executed)
  fuzzing_time_percent = 100 * actual_duration / float(expected_duration)
  stat_overrides = {
      'timeout_limit': int(timeout_limit),
      'expected_duration': expected_duration,
      'actual_duration': actual_duration,
      'fuzzing_time_percent': fuzzing_time_percent,
  }

  # Remove fuzzing arguments before merge and dictionary analysis step.
  remove_fuzzing_arguments(arguments)

  # Make a decision on whether merge step is needed at all. If there are no
  # new units added by libFuzzer run, then no need to do merge at all.
  new_units_added = shell.get_directory_file_count(new_testcases_directory)
  merge_error = None
  if new_units_added:
    # Merge the new units with the initial corpus.
    if corpus_directory not in corpus_directories:
      corpus_directories.append(corpus_directory)

    # If this times out, it's possible that we will miss some units. However, if
    # we're taking >10 minutes to load/merge the corpus something is going very
    # wrong and we probably don't want to make things worse by adding units
    # anyway.

    merge_tmp_dir = None
    if not use_minijail:
      merge_tmp_dir = os.path.join(fuzzer_utils.get_temp_dir(), 'merge_workdir')
      engine_common.recreate_directory(merge_tmp_dir)

    old_corpus_len = shell.get_directory_file_count(corpus_directory)
    merge_directory = create_merge_directory()
    corpus_directories.insert(0, merge_directory)

    if use_minijail:
      bind_corpus_dirs(minijail_chroot, [merge_directory])

    merge_result = runner.merge(
        corpus_directories,
        merge_timeout=engine_common.get_merge_timeout(DEFAULT_MERGE_TIMEOUT),
        tmp_dir=merge_tmp_dir,
        additional_args=arguments)

    move_mergeable_units(merge_directory, corpus_directory)
    new_corpus_len = shell.get_directory_file_count(corpus_directory)
    new_units_added = 0

    merge_error = None
    if merge_result.timed_out:
      merge_error = 'Merging new testcases timed out:'
    elif merge_result.return_code != 0:
      merge_error = 'Merging new testcases failed:'
    else:
      new_units_added = new_corpus_len - old_corpus_len

    stat_overrides['new_units_added'] = new_units_added

    if merge_result.output:
      stat_overrides.update(
          stats.parse_stats_from_merge_log(merge_result.output.splitlines()))
  else:
    stat_overrides['new_units_added'] = 0
    logs.log('Skipped corpus merge since no new units added by fuzzing.')

  # Get corpus size after merge. This removes the duplicate units that were
  # created during this fuzzing session.
  # TODO(flowerhack): Remove this workaround once we can handle corpus sync.
  if environment.platform() != 'FUCHSIA':
    stat_overrides['corpus_size'] = shell.get_directory_file_count(
        corpus_directory)

  # Delete all corpus directories except for the main one. These were temporary
  # directories to store new testcase mutations and have already been merged to
  # main corpus directory.
  if corpus_directory in corpus_directories:
    corpus_directories.remove(corpus_directory)
  for directory in corpus_directories:
    shutil.rmtree(directory, ignore_errors=True)

  if use_minijail:
    unbind_corpus_dirs(minijail_chroot, corpus_directories)

  # Apply overridden stats to the parsed stats prior to dumping.
  parsed_stats.update(stat_overrides)

  # Dump stats data for further uploading to BigQuery.
  engine_common.dump_big_query_data(parsed_stats, testcase_file_path, command)

  # Add custom crash state based on fuzzer name (if needed).
  add_custom_crash_state_if_needed(fuzzer_name, log_lines, parsed_stats)
  for line in log_lines:
    print(line)

  # Add fuzzing strategies used.
  print(engine_common.format_fuzzing_strategies(
      strategy_info.fuzzing_strategies))

  # Add merge error (if any).
  if merge_error:
    print(data_types.CRASH_STACKTRACE_END_MARKER)
    print(merge_error)
    print('Command:',
          get_printable_command(merge_result.command, fuzzer_path,
                                use_minijail))
    print(merge_result.output)

  analyze_and_update_recommended_dictionary(runner, fuzzer_name, log_lines,
                                            corpus_directory, arguments)

  # Close minijail chroot.
  if use_minijail:
    minijail_chroot.close()

  # Record the stats to make them easily searchable in stackdriver.
  if new_units_added:
    logs.log(
        'New units added to corpus: %d.' % new_units_added, stats=parsed_stats)
  else:
    logs.log('No new units found.', stats=parsed_stats)